The present invention relates to a leadframe which is used as an assembly member of electronic parts, for example, a semiconductor device.
The packaging density of semiconductor devices has been increasing in recent years. Under such circumstances, the external size of packages of semiconductor elements has been decreasing year by year. In consequence, leadframes that are used as assembly members of semiconductor devices have also decreased in size. More specifically, the distance from a resin molding line to a dam bar, which was 0.25 mm in the past, has decreased to about 0.18 mm. Thus, the dam bar and the package line have become closer to each other.
In addition, the pitch of outer leads of leadframes has been decreasing year by year, i.e., from 0.65 mm to 0.55 mm, 0.5 mm and 0.35 mm. With the decrease in the pitch of outer leads, the thickness of outer leads has also decreased, i.e., 0.25 mm to 0.07 mm.
Under such circumstances, outer leads are produced with a width of from 0.3 mm to 0.1 mm, so that dam bars are cut off with a considerably thin cutting punch of 0.25 mm to 0.08 mm in width.
However, since the dam bars of the conventional leadframes have a relatively large thickness, such a thin cutting punch is likely to chip off, so that the lifetime of the cutting punch is shortened.
If the cutting punch chips off, a large shear droop a is induced on the cut surface of the dam bar, as shown in FIG. 21. Such a shear droop a forms large burr, resulting in degradation of the external appearance.
In addition, since the dam bar is distorted when it is cut, the leadframe may be deformed.
In addition, when the resin material that is present in between the dam bar and the molding line is cut, the resin burr may scatter, causing problems.